Jun-ichiro Koizumi and Morihiro Hosokawa made the announcement at a news conference on January 10th.
Koizumi said that given what Prime Minister Shinzo Abe's administration has been saying and doing, it will be difficult to promote a policy of zero nuclear plants under the present administration.
But he said it is possible to achieve the goal in the near future with the support from a majority of the Japanese public, and he wants to push for a nationwide movement.
Four years ago, when Hosokawa ran in the Tokyo gubernatorial election, he joined with Koizumi to call for scrapping nuclear power plants.
During the race, Hosokawa said Japan will fail to keep up with the world unless it opts to live without nuclear power. Koizumi said if Hosokawa is elected governor of Tokyo, it will be possible to break with the idea that Japan needs nuclear power to survive.
Though Hosokawa was defeated, the two former leaders continued to call for a zero nuclear-power policy.
At the press conference in January, Koizumi and Hosokawa gave the outline for a bill. It was written by a private group that promotes renewable energy sources. Koizumi and Hosokawa are advisers to the group.
The outline says the government should scrap nuclear power immediately and adopt a national policy of using renewable energy sources for all electric power generation by 2050.
"I am disturbed by the forces trying to maintain nuclear power no matter how much it costs," Koizumi said. "I believe, this year, there will be political parties that rise in the Diet to accept the people's call for zero nuclear power. Politics will change if there is the will to do so. Our group will cooperate with any parties that support scrapping nuclear power and make every effort to promote renewable energy. "
Koizumi was asked if he will make this appeal to candidates in the election slated for September to choose the next Liberal Democratic Party president.
He said he will devote his efforts to changing the general public's opinion rather than trying to reach out to political parties or politicians.
After the news conference, the group called on parties to submit a bill in line with their proposal to the Diet.
Regarding the outline from the former prime ministers, Chief Cabinet Secretary Yoshihide Suga said he will not comment on it as he does not know its specific details.
He added that the government's position is to make efforts to promote energy-saving measures and introduce renewable energy sources as much as possible to reduce dependence on nuclear power.
Suga also said the government's stance is consistent with restarting reactors only when they are confirmed to be safe by the Nuclear Regulation Authority, and with the support of local people.